Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory.
Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Common uses for flash memory include personal computers, personal digital assistants (PDAs), digital cameras, and cellular telephones. Program code and system data such as a basic input/output system (BIOS) are typically stored in flash memory devices for use in personal computer systems.
As electronic systems and software become more complex, they require additional memory capacity. However, as flash memory device sizes increase, the time and power required to program the memory also increases. This can decrease system performance.
NOR-type flash memory devices typically use a Channel Hot Electron (CHE) method of programming. CHE involves a high current on the bitline and through the cell, between the drain and source, that is being programmed. The bitline current also consists of the summed parasitic current from all other cells, on the same bitline, that are intended to be in an “off” state and yet still leak some current. The current leakage increases overall current draw from the bitline charge pump and also increases the voltage drop in the bitline path due to the additional IR drop. This results in lower programming efficiency.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for more efficient programming of a flash memory transistor.